A survey of 1,106 senior decision-makers in business found nearly 60 percent believed women should say whether they were pregnant when applying for a job, according to the Equality and Human Rights Commission (EHRC), which commissioned the research.

More than a third said it was appropriate to ask candidates about their future plans to have children, and nearly half thought it was reasonable to ask job-seeking women whether they had young children, the survey found.

"It is a depressing reality that, when it comes to the rights of pregnant woman and new mothers in the workplace, we are still living in the dark ages," Rebecca Hilsenrath, chief executive of the EHRC, said in a statement.

A third of those surveyed believed new mothers were "generally less interested in career progression" compared with other workers, while four in 10 said that pregnancy put "an unnecessary cost burden" on the employer.

British law prohibits employers from rejecting candidates because they are pregnant or might become pregnant.

The EHRC urged businesses to work towards eliminating such discriminatory attitudes and urged them to join a campaign to improve workplace conditions for pregnant women and new parents.

Yet advocates said a voluntary pledge for firms was on its own unlikely to curb discrimination, and said policymakers must strengthen legal protections for pregnant women and new mothers.

"It's unfortunately the case that asking employers to do the right thing is not sufficient," Rosalind Bragg, director of Maternity Action, told the Thomson Reuters Foundation.

"We do need to have much more aggressive efforts from government to address the very poor behaviour of many dinosaur employers who are not complying with their legal obligations."

In a 2017 review of modern employment practices, Britain pledged to examine redundancy protections for pregnant women and new mothers. It did not provide a timeline for the process.